===== Creating a video loopback device (Linux) =====
  * v4l2loopback works in ubuntu 20.04 but the binary needs to be compiled:
    * get the headers for the kernel version you are using
    * from the package manager install ''v4l2loopback-source''
    * ''cd /usr/src/v4l2loopback-0.12.3/''
    * ''sudo make''
  * ''sudo modprobe v4l2loopback''
  * to create 2 devices ''modprobe v4l2loopback devices=2'' (untested but in the docs)
===== writing to loopback device with opencv Python =====
  * import v4l2
    * [[https://github.com/AlexJinlei/python-v4l2/issues/5|fix bug]]
  * the magic sauce is [[https://pypi.org/project/virtualvideo/|virtualvideo]]. Trying to convert/write raw video seemed like a dead end:
    * ''import virtualvideo''
    * in the example code: ''fvd.init_output(2, 1280, 720, fps=30)'' the first parameter (2) is the video #
 
===== writing to loopback device with Pd/Gem =====
  * ''|pix_record|'' is the magic sauce. Send it codec 33 and open file ''/dev/video[NUMBER]''
    * {{ :lwc:multimedia_and_graphics:test1.pd |example}}

===== OpenCV (cv2) wiith Pycharm ====
For code completion to work you need to downgrade openCV :(
  * from the terminal inside Pycharm: ''pip install --force-reinstall --no-cache -U opencv-python==4.5.5.62''